The program project grant Neutralizing Antibody (NAb) and AAV FIX Gene Therapy is a timely focused application centered around advancing exciting new clinical data that self complementary (sc)AAV Factor IX (FIX) vectors are showing promising success in clinical studies (5-8% >1yr). To further advance these successes, we have assembled a multidisciplinary approach to understand, address, and resolve the role of pre-existing NAb to AAV capsid (over 80% of general population). A primary focus of PPG relates to molecular interactions between viral capsid in antibody response, engineering next generation vectors, and development and testing in novel NAb positive animal models. This PPG consists of 4 projects and 3 cores. Project 1 FIX Gene Therapy and Role of AAV NAb (PI - Dr. R. Jude Samulski) will capitalize on the availability of St. Jude FIX trial serum samples, humanized mouse models and peptide library to understand relationship between capsid antigen presentation and Ab response. Project 2 Humanizing AAV Vectors for Gene Therapy (PI- Dr. Aravind Asokan) will focus on engineering and utilizing novel AAV vectors in an effort to avoid NAb. Project 3 Intra-articular AAV to Circumvent Systemic Neutralization (PI - Dr. Paul Monahan) will utilize PPG gene transfer reagents to understand and prevent joint complications of hemophilia in animal models with pre-existing NAb. Project 4 Generation of a Model of Hemophilia B and AAV Resistant Primates (PIs Bruce Sullenger/Dougald Monroe): will use aptamer technology to generate and validate hemophilia in Ab+ non-human primate model for gene correction with PPG vectors, along with Administrative core (Pl-Dr. Samulski, Co-Dr. Monahan), vector and animal cores (Pls-Drs. Beecham & Li). This PPG is composed of unique group of researchers with expertise in biochemistry (Dr. Monroe), molecular biology (Dr. Sullenger), virology (Drs. Asokan & Samulski), and clinical hematology (Dr. Monahan) working synergistically to bring direct benefit of vector development (AAV), molecular therapeutics (sc-opt FIX and opt FVlll), and novel NAb non-human primate hemophilic model (aptamer) to bleeding disorders. The long-term objective of this PPG is to advance basic understanding of vector-cell-animal model interactions for safe gene delivery.